1. Technical Field
The present invention relates to a suction nozzle, and more particularly, relates to a suction nozzle for holding a component by suction used in a component mounting apparatus for mounting a component, such as an electronic component, on a circuit formation object such as a circuit board.
2. Description of the Related Art
FIG. 13 illustrates a conventional suction nozzle 1 used for holding an electronic component B by suction in an electronic component mounting apparatus.
The suction nozzle 1 includes: an outer nozzle member 2 having a first suction passage 2a; a nozzle body 3 provided to be displaceable with respect to the outer nozzle member 2 and having a second suction passage 3a for communicating with the first suction passage 2a; and a spring 4 provided between the outer nozzle member 2 and the nozzle body 3 for elastically urging the nozzle body 3 toward a predetermined side (downward side in FIG. 13) in the displacement direction (upward and downward in FIG. 13). The second suction passage 3a extends in the displacement direction of the nozzle body 3. One end (lower end in FIG. 13) of the second suction passage 3a is open at a front end face 3b (lower end face in FIG. 13) of the nozzle body 3 in the displacement direction, whereas the other end (upper end in FIG. 13) thereof is open at a rear end face 3c (upper end face in FIG. 13) of the nozzle body 3 in the displacement direction to allow communication with the first suction passage 2a. 
The suction nozzle 1 is removably attached to a nozzle shaft 6 of a mounting head section 5 of the electronic component mounting apparatus by a nozzle holder 7. The nozzle holder 7 includes an inner sleeve 7b holding balls 7a inside and an outer sleeve 7c into which the inner sleeve 7b is pressed. The balls 7a are fitted into engaging concave 2b formed on the outer nozzle member 2, and thus the suction nozzle 1 is secured to the nozzle shaft 6.
A suction passage 6a of the nozzle shaft 6 is in communication with a vacuum suction pump 8. Thus, the electronic component B is held by being sucked at the front end face 3b of the nozzle body 3 with a suction force of the vacuum suction pump 8 acting through the suction passage 6a of the nozzle shaft 6, the first suction passage 2a of the outer nozzle member 2, and the second suction passage 3a of the nozzle body 3. The nozzle shaft 6 is mechanically connected to an elevation mechanism 9 and a rotation drive mechanism 10. The suction nozzle 1 therefore moves up and down together with the nozzle shaft 6 by the elevation mechanism 9, and rotates around its axis together with the nozzle shaft 6 by the rotation drive mechanism 9.
When the electronic component B is to be picked up by suction from a component feeder section (not shown) of the electronic component mounting apparatus, the suction nozzle 1 is lowered to a predetermined height position (suction height position), where the front end face 3b of the nozzle body 3 comes into contact with the electronic component B. The electronic component B is then sucked to the front end face 3b of the nozzle body 3 with the suction force of the vacuum suction pump 8. The suction nozzle 1 holding the electronic component B by suction is lifted to the original height position.
When the electronic component B is to be placed on a circuit board (not shown), the suction nozzle 1 is lowered to a predetermined height position (placement height position), where the electronic component B comes into contact with the circuit board. The suction nozzle 1 is further lowered to apply a load to the electronic component B that is already in contact with the circuit board. By this application of a load, the electronic component B is placed on the circuit board.
The spring 4 is provided for absorbing the impact applied to the component during suction and placement of the component. More specifically, the spring 4 absorbs the impact applied to the component B when the component B comes into contact with the nozzle body 3 during the component suction operation. The spring 4 also absorbs the impact applied to the component B when the component B comes into contact with the circuit board during the component mounting operation. In consideration of only this impact absorbing function, the urging force of the spring 4 is preferably as small as possible.
During the suction of the electronic component B by the suction nozzle 1, the suction force provided by the vacuum suction pump 8 also acts on the rear end face 3c (upper end face in FIG. 13) of the nozzle body 3, urging the nozzle body 3 in the direction in which the spring 4 is compressed. If this suction force causes the nozzle body 3 to be displaced and changes the height position of the front end face 3b of the nozzle body 3, a suction error and a placement error of the electronic component B may occur. In order to avoid this displacement of the nozzle body 3 with respect to the outer nozzle member 2 due to the suction force, the urging force of the spring 4 is conventionally set at a relatively large value (for example, 3.92 to 5.88 N (400 to 600 gf)) so that the urging force can resist the suction force acting on the nozzle body 3.
However, the large urging force of the spring 4 inevitably reduces the impact absorbing function. Namely, the large urging force of the spring 4 results ins a relatively high load being applied to the electronic component B when the suction nozzle 1 comes into contact with the electronic component B during the component suction operation. Likewise, a relatively high load is applied to the electronic component B when the electronic component comes into contact with the circuit board during the component placement operation.
Some recent electronic components, on a back surface thereof, have solder balls which are to be crushed to an appropriate diameter by a load during placement. Such small-size electronic components must be placed with a low load. If a high load is applied to such electronic components during placement, the solder balls will be crushed excessively. In view of this point, the above-described conventional suction nozzle 1 is not suitable for mounting the small-size electronic components having the solder balls on the back surface thereof.